Expression Cloning and Characterization of a Novel Glycosylphosphatidylinositol-anchored High Density Lipoprotein-binding Protein, GPI-HBP1

Ryoichi X Ioka,Man-Jong Kang,Shin Kamiyama,Dong-Ho Kim,Kenta Magoori,Akihisa Kamataki,Yuichiro Ito,Yumiko A Takei,Masako Sasaki,Takashi Suzuki,Hironobu Sasano,Sadao Takahashi,Juro Sakai,Takahiro Fujino,Tokuo T Yamamoto

doi:10.1074/jbc.m211932200

Abstract

By expression cloning using fluorescent-labeled high density lipoprotein (HDL), we isolated two clones that conferred the cell surface binding of HDL. Nucleotide sequence of the two clones revealed that one corresponds to scavenger receptor class B, type 1 (SRBI) and the other encoded a novel protein with 228 amino acids. The primary structure of the newly identified HDL-binding protein resembles GPI-anchored proteins consisting of an N-terminal signal sequence, an acidic region with a cluster of aspartate and glutamate residues, an Ly-6 motif highly conserved among the lymphocyte antigen family, and a C-terminal hydrophobic region. This newly identified HDL-binding protein designated GPI-anchored HDL-binding protein 1 (GPI-HBP1), was susceptible to phosphatidylinositol-specific phospholipase C treatment and binds HDL with high affinity (calculated K(d) = 2-3 microg/ml). Similar to SRBI, GPI-HBP1 mediates selective lipid uptake but not the protein component of HDL. Among various ligands for SRBI, HDL was most preferentially bound to GPI-HBP1. In contrast to SRBI, GPI-HBP1 lacked HDL-dependent cholesterol efflux. The GPI-HBP1 transcripts were detected with the highest levels in heart and, to a much lesser extent, in lung and liver. In situ hybridization revealed the accumulation of GPI-HBP1 transcripts in cardiac muscle cells, hepatic Kupffer cells and sinusoidal endothelium, and bronchial epithelium and alveolar macrophages in the lung.

Highlights

By expression cloning using fluorescent-labeled high density lipoprotein (HDL), we isolated two clones that conferred the cell surface binding of HDL
Several HDL-binding proteins have been identified including class B type I scavenger receptor (SRBI) [2, 3], two candidate hepatic HDL receptors designated HDL-binding proteins 1 and 2 [4, 5], 80- and 130-kDa GPI-anchored HDL-binding proteins expressed in human macrophages [6], 110-kDa GPI-anchored HDL-binding protein expressed in HepG2 cells [7], and recently characterized 95-kDa HDL-binding protein [8]
Only SRBI appears to be a physiological HDL receptor based on the selective uptake of cholesterol esters into cells and the efflux of cholesterol from cells to HDL mediated by SRBI [1]

Summary

Introduction

By expression cloning using fluorescent-labeled high density lipoprotein (HDL), we isolated two clones that conferred the cell surface binding of HDL. Similar to SRBI, GPI-HBP1 mediates selective lipid uptake but not the protein component of HDL. We identified a novel HDL-binding protein by expression cloning from a murine hepatic cDNA library.

Results

Conclusion